1. Field of the Invention
The present invention provides methods and compositions for forming permeable cement sand screens in wells to prevent sand from flowing into the well with produced hydrocarbons and other fluids.
2. Description of the Prior Art
Oil, gas and water producing wells are often completed in unconsolidated subterranean formations containing loose or incompetent sand which flows into the well bores with produced fluids. The presence of the sand in the produced fluids rapidly erodes metal tubular goods and other production equipment which often substantially increases the costs of operating the wells.
Gravel packs have heretofore been utilized in wells to prevent the production of sand. Such gravel packs are comprised of a pack of gravel such as graded sand which is placed in the annulus between a perforated or slotted liner or screen and the walls of a well bore in the fluid producing zone. The resulting structure provides a barrier to migrating sand from the producing zone while allowing the flow of produced fluids. Gravel packs have successfully prevented the production of sand with formation fluids, but they often fail and require replacement. For example, gravel packs frequently fail due to the deterioration of the perforated or slotted liner or screen as a result of corrosion or the like. The initial installation of a gravel pack adds considerable expense to the cost of completing a well and the removal and replacement of a failed gravel pack is even more costly.
Thus, there are continuing needs for improved methods of preventing the production of formation sand, fines and the like with produced subterranean formation fluids.
The present invention provides improved methods and compositions for forming permeable cement sand screens in well bores which meet the needs described above and overcome the deficiencies of the prior art. The methods of the invention are basically comprised of the following steps. A cement composition which can be foamed if required is prepared comprised of a hydraulic cement, a particulate cross-linked aqueous gel having a size in the range of from about 100 microns to about 3000 microns containing an internal temperature activated breaker which causes the gel to break into a liquid, a particulate dehydrated cross-linked aqueous gel having a size in the range of from about 40 microns to about 500 microns containing an internal temperature activated breaker which causes the gel to break into a liquid and water present in an amount sufficient to form a slurry. If the cement composition is foamed, a gas in an amount sufficient to form a foam and a mixture of foaming and foam stabilizing surfactants are included in the cement composition. The cement composition is then placed in a well bore adjacent to a fluid producing zone therein, the cement composition is allowed to set and the particulate cross-linked aqueous gels containing internal temperature activated breakers are allowed to break whereby a permeated set cement composition is formed in the fluid producing zone. An acid solution is then introduced into the well bore into contact with the permeated set cement whereby the acid solution flows through the permeations in the set cement and dissolves any portions of the set cement blocking the permeations.
The permeable set cement in the well bore functions as a sand screen, i.e., the permeable cement allows produced fluids to flow into the well bore, but prevents formation sand and the like from flowing therein. The permeable cement sand screen can completely fill the portion of the well bore adjacent to the fluid producing zone whereby the permeable cement sand screen bonds to the walls of the well bore. The permeable cement sand screen cannot be bypassed and does not readily deteriorate.
In an alternate embodiment of the present invention which is utilized when it is desired to form a permeable cement composition sand screen of high strength and integrity that includes an extension of the well bore therethrough adjacent to an open-hole fluid producing zone below a cased well bore, an expandable slotted pipe is utilized. That is, an expandable slotted pipe is placed in the fluid producing zone below or adjacent to the end of casing in a well bore. If required to provide enough space between the expanded slotted pipe and the walls of the well bore, the well bore below the casing can be enlarged using a reaming or hydrojetting technique prior to placing the expandable slotted pipe in the fluid producing zone. After placement, the slotted pipe is expanded to the internal size of the casing in the well bore. A cement composition of the present invention as described above is then prepared and the cement composition is placed in the well bore adjacent to the fluid producing zone within the expanded slotted pipe therein, between the expanded slotted pipe and the open-hole well bore and within any voids or fractures in the producing zone. The cement composition is allowed to set and the particulate cross-linked aqueous gels containing internal temperature activated breakers to break whereby a permeated set cement composition is formed in the open-hole producing zone. The set permeable cement composition within the expanded slotted pipe is drilled out leaving a high strength permeable cement composition sand screen in the producing zone. Thereafter, an acid solution is introduced by way of the well bore into contact with the permeated set cement whereby the acid solution flows through the permeations in the set cement and dissolves any portions of the set cement blocking the permeations.
The compositions of this invention for forming a permeable cement sand screen in a well bore are basically comprised of a hydraulic cement, a particulate cross-linked aqueous gel having a size in the range of from about 100 microns to about 3000 microns containing an internal temperature activated breaker which causes the gel to break into a liquid, a particulate dehydrated cross-linked aqueous gel having a size in the range of from about 40 microns to about 500 microns containing an internal temperature activated breaker which causes the gel to break into a liquid, and water present in an amount sufficient to form a slurry. If the cement composition should be foamed to reduce its density or for other reasons, the cement composition can include a gas present in an amount sufficient to form a foam and a mixture of foaming and foam stabilizing surfactants.
It is, therefore, a general object of the present invention to provide improved methods and compositions for forming permeable cement sand screens in well bores
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.